Over the last years, considerable research has been conducted to develop and apply edible films and coatings made from a variety of agricultural commodities and/or wastes of food product industrialization. Such biopolymers include polysaccharides, proteins, and their blends. These materials present the possibility of being carriers of different additives, such as antimicrobial, antioxidant, nutraceuticals, and flavorings agents. In particular, the use of edibles films and coatings containing antimicrobials has demonstrated to be a useful tool as a stress factor to protect foodstuff against spoilage flora and to decrease the risk of pathogen growth. The more commonly antimicrobials used are organic acids, chitosan, nisin, the lactoperoxidase system, and some plant extracts and their essential oils. For the selection of an antimicrobial, it must be considered the effectiveness against the target microorganism and also the possible interactions among the antimicrobial, the film-forming biopolymer, and other food components present. These interactions can modify the antimicrobial activity and the characteristics of the film being these key factors for the development of antimicrobial films and coatings. The main objective of this article is to review the bibliography of the last years concerning the main hydrocolloids and antimicrobials used for developing edible films and coatings, the methods used to evaluate the antimicrobial activity, the applications and the legislation concerning edible films and coatings. Also, the different strategies related to the modification of structural characteristics and the future trends in the development are discussed. The information update will help to improve the design, development, and application of edible films and coatings tending to increase the safety and quality of food products and to prepare for food legislation changes that might be necessary while identifying future trends concerning a better functionality of edible films thought as a stress factor for lengthening shelf life of food products.

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Development of Edible Films and Coatings with Antimicrobial Activity

Petroleum-based plastics have replaced many natural materials in their former applications. With their excellent properties, they have found widespread uses in almost every area of human life. However, the high recalcitrance of many synthetic plastics results in their long persistence in the environment, and the growing amount of plastic waste ending up in landfills and in the oceans has become a global concern. In recent years, a number of microbial enzymes capable of modifying or degrading recalcitrant synthetic polymers have been identified. They are emerging as candidates for the development of biocatalytic plastic recycling processes, by which valuable raw materials can be recovered in an environmentally sustainable way. This review is focused on microbial biocatalysts involved in the degradation of the synthetic plastics polyethylene, polystyrene, polyurethane and polyethylene terephthalate (PET). Recent progress in the application of polyester hydrolases for the recovery of PET building blocks and challenges for the application of these enzymes in alternative plastic waste recycling processes will be discussed.

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Microbial enzymes for the recycling of recalcitrant petroleum-based plastics: how far are we?

Fighting bacterial resistance is one of the concerns in modern days, as antibiotics remain the main resource of bacterial control. Data shows that for every antibiotic developed, there is a microorganism that becomes resistant to it. Natural polymers, as the source of antibacterial agents, offer a new way to fight bacterial infection. The advantage over conventional synthetic antibiotics is that natural antimicrobial agents are biocompatible, non-toxic, and inexpensive. Chitosan is one of the natural polymers that represent a very promising source for the development of antimicrobial agents. In addition, chitosan is biodegradable, non-toxic, and most importantly, promotes wound healing, features that makes it suitable as a starting material for wound dressings. This paper reviews the antimicrobial properties of chitosan and describes the mechanisms of action toward microbial cells as well as the interactions with mammalian cells in terms of wound healing process. Finally, the applications of chitosan as a wound-dressing material are discussed along with the current status of chitosan-based wound dressings existing on the market.

Chitosan as a Wound Dressing Starting Material: Antimicrobial Properties and Mode of Action

Bio-inspired adhesive catechol-conjugated chitosan for biomedical applications: A mini review

Synthetic plastics are pivotal in our current lifestyle and therefore, its accumulation is a major concern for environment and human health. Petroleum-derived (petro-)polymers such as polyethylene (PE), polyethylene terephthalate (PET), polyurethane (PU), polystyrene (PS), polypropylene (PP), and polyvinyl chloride (PVC) are extremely recalcitrant to natural biodegradation pathways. Some microorganisms with the ability to degrade petro-polymers under in vitro conditions have been isolated and characterized. In some cases, the enzymes expressed by these microbes have been cloned and sequenced. The rate of polymer biodegradation depends on several factors including chemical structures, molecular weights, and degrees of crystallinity. Polymers are large molecules having both regular crystals (crystalline region) and irregular groups (amorphous region), where the latter provides polymers with flexibility. Highly crystalline polymers like polyethylene (95%), are rigid with a low capacity to resist impacts. PET-based plastics possess a high degree of crystallinity (30-50%), which is one of the principal reasons for their low rate of microbial degradation, which is projected to take more than 50 years for complete degraded in the natural environment, and hundreds of years if discarded into the oceans, due to their lower temperature and oxygen availability. The enzymatic degradation occurs in two stages: adsorption of enzymes on the polymer surface, followed by hydro-peroxidation/hydrolysis of the bonds. The sources of plastic-degrading enzymes can be found in microorganisms from various environments as well as digestive intestine of some invertebrates. Microbial and enzymatic degradation of waste petro-plastics is a promising strategy for depolymerization of waste petro-plastics into polymer monomers for recycling, or to covert waste plastics into higher value bioproducts, such as biodegradable polymers via mineralization. The objective of this review is to outline the advances made in the microbial degradation of synthetic plastics and, overview the enzymes involved in biodegradation.

/pdf/microbial-and-enzymatic-degradation-of-synthetic-plastics-12s5r99574.pdf

Microbial and Enzymatic Degradation of Synthetic Plastics

Antimicrobial and antioxidant properties of chitosan enzymatically functionalized with flavonoids

Summary In this work the effect of crosslinking the enzyme esperase (E.C. 3.4.21.62) and the proteins bovine serum albumin and casein with the bifunctional compound glutaraldehyde on molecular mass increase was studied. Two common techniques for measuring molecular mass of proteins were used: SEC and SDS-PAGE. These techniques revealed that the proteins bovine albumin and casein, when subjected to chemical crosslinking with glutaraldehyde, volume fraction 0.25 %, increased their molecular mass by 20- and 40-fold, respectively. It was also observed that Mr increased proportionally to the increase of glutaraldehyde concentration in the solution, and that the addition of glutaraldehyde should be done slowly, in small amounts, in order to attain bigger protein aggregates. When the proteolytic enzyme esperase was subjected to glutaraldehyde, no increase in its Mr was achieved. Several assumptions can be made to explain these results, the most reasonable being the low amount of free lysine groups available for crosslinking. This study confirms that glutaraldehyde is not an adequate crosslinker for esperase.

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Chemical Modifications on Proteins Using Glutaraldehyde

A polyethylene terephthalate (PET) model substrate, bis-(benzoyloxyethyl)terephthalate (3PET), was used to screen for micro-organisms producing enzymes hydrolyzing PET. From this screen, a strain growing on 3PET was isolated and identified as Penicillium citrinum. The polyesterase responsible for 3PET and PET hydrolysis was purified to electrophoretic homogeneity. The polyesterase had a molecular weight of 14.1 kDa, and the Km and Kcat values on 4-nitrophenyl butyrate were 0.57 mM and 0.21 s−1, respectively. Highest enzyme activities were obtained when P. citrinum was grown on a medium containing cutin, which was hydrolyzed by the polyesterase. Surface hydrolysis of PET with the enzyme lead to an increase in hydrophilicity based on rising height (+5.1 cm) and drop dissipation measurements (55 s). Both from PET and 3PET bis-(2-hydroxyethyl)terephthalate and mono-(2-hydroxyethyl)terephthalate were released, while only low amounts of terephthalic acid were liberated.

Hydrolysis of PET and bis-(benzoyloxyethyl) terephthalate with a new polyesterase from Penicillium citrinum

https://repositorium.sdum.uminho.pt/bitstream/1822/13561/1/A%20novel%20metalloprotease%20from%20Bacillus%20cereus%20for%20protein%20fibre%20processing.pdf

A novel metalloprotease from Bacillus cereus for protein fibre processing

From a screening for the production of new proteases specific for cuticle scales, Beauveria brongniartii was selected producing an alkaline Ca(++) dependent protease. The purified had a molecular weight of 27 kDa and a pI value of 8.0. Substrate specificities of model substrates (wool with partially removed cuticles treated with SDS) were analyzed by protein release, dissolved organic carbon (DOC) and nitrogen analysis. The C/N ratio of released material turned out to be a good parameter to determine the site of action of proteases on fibres. Compared to other enzymes, the fungal protease preferentially hydrolyzed cuticle scales and has thus a potential for anti-shrinking pre-treatment of wool fabrics.

/pdf/a-new-cuticle-scale-hydrolysing-protease-from-beauveria-1yw1aiojum.pdf

Fernanda Sousa

Papers

Antimicrobial and antioxidant properties of chitosan enzymatically functionalized with flavonoids

Chemical Modifications on Proteins Using Glutaraldehyde

Hydrolysis of PET and bis-(benzoyloxyethyl) terephthalate with a new polyesterase from Penicillium citrinum

A novel metalloprotease from Bacillus cereus for protein fibre processing

A new cuticle scale hydrolysing protease from Beauveria brongniartii.